The Office of Health and Environmental Research (OHER) has supported and continues to support development of computational approaches in biology and medicine. OHER's Radiological and Chemical Physics Program initiated development of computational approaches to determine the effects produced by radiation of different quality (such as high energy electrons, protons, helium and other heavy ions, etc. ) in a variety of materials of biological interest-such as water, polymers and DNA; these include molecular excitations and sub-excitations and the production of ionization and their spatial and temporal distribution. In the past several years, significant advances have been made in computational methods for this purpose. In particular, codes based on Monte Carlo techniques have .been developed that provide a realistic description of track-structure produced by charged particles. In addition, the codes have become sufficiently sophisticated so that it is now possible to calculate the spatial and temporal distribution of energy deposition patterns in small volumes of subnanometer and nanometer dimensions. These dimensions or resolution levels are relevant for our understanding of mechanisms at the molecular level by which radiations affect biological systems. Since the Monte Carlo track structure codes for use in radiation chemistry and radiation biology are still in the developmental stage, a number of investigators have been exploring different strategies for improving these codes."

The fundamental understanding of the production of biological effects by ionizing radiation may well be one of the most important scientific objectives of mankind; such understanding could lead to the effective and safe utilization of the nuclear energy option. In addition, this knowledge will be of immense value in such diverse fields as radiation therapy and diagnosis and in the space program. To achieve the above stated objective, the U. S. Department of Energy (DOE) and its predecessors embarked upon a fundamental interdisciplinary research program some 35 years ago. A critical component of this program is the Radiological and Chemical Physics Program (RCPP). When the RCPP was established, there was very little basic knowledge in the fields of physics, chemistry, and biology that could be directly applied to understanding the effects of radiation on biological systems. Progress of the RCPP program in its first 15 years was documented in the proceedings of a conference held at Airlie, Virginia, in 1972. At this conference, it was clear that considerable progr:ess had been made in research on the physical and chemical processes in well-characterized systems that could be used to understand biological effects. During this period of time, most physical knowledge was obtained for the gas phase because the technology and instru mentation had not progressed to the point that measurements could be made in liquids more characteristic of biological materials.

The Office of Health and Environmental Research (OHER) has supported and continues to support development of computational approaches in biology and medicine. OHER's Radiological and Chemical Physics Program initiated development of computational approaches to determine the effects produced by radiation of different quality (such as high energy electrons, protons, helium and other heavy ions, etc. ) in a variety of materials of biological interest-such as water, polymers and DNA; these include molecular excitations and sub-excitations and the production of ionization and their spatial and temporal distribution. In the past several years, significant advances have been made in computational methods for this purpose. In particular, codes based on Monte Carlo techniques have .been developed that provide a realistic description of track-structure produced by charged particles. In addition, the codes have become sufficiently sophisticated so that it is now possible to calculate the spatial and temporal distribution of energy deposition patterns in small volumes of subnanometer and nanometer dimensions. These dimensions or resolution levels are relevant for our understanding of mechanisms at the molecular level by which radiations affect biological systems. Since the Monte Carlo track structure codes for use in radiation chemistry and radiation biology are still in the developmental stage, a number of investigators have been exploring different strategies for improving these codes."